Phase shift beam tube neutralizer and modulator



Jan. 24; 1967 'G. M. w. BADGER 3,300,73

PHASE SHIFT BEAM TUBE NEUTRALIZER ANDMODULATOR Filed D90. 51, 1962GEORGE MW. BADGER INVENTOR.

ATTORNEY United States Patent Office 3,300,735 Patented Jan. 24, 1967 t'f California on Filed Dec. 31, 1962, Ser. No. 248,499

8 Claims. (Cl. 3327) This invention relates to a phase shift neutralizerand more particularly to apparatus for neutralizing phase shlft due tovelocity variation in the beam of a beam type tube such as a klystron.

In beam type tubes, there is a space charge variationrn the beam itselfdue to the negative charge on the individual electrons within the beam.As the beam passes through accelerating electrodes, the acceleratingvoltage affects those electrons at the outer surface of the beam to agreater extent than the electrons at the center of the beam. As the beambecomes more dense, the degree of penetration to the interior isreduced. Consequently, there results a velocity variation across thebeam wh1ch is dependent upon the beam density. As the beam becomesdenser, the average velocity of the beam for the same acceleratingvoltage is reduced. In a typical application, the change in average beamvelocity can be as much as 5%.

In a modulating anode type beam tube, there is generally provided asource of electrons, a modulating anode which controls the beam density,an accelerating anode which controls the velocity of the beam, and aradio frequency section which interacts with the beam to form the outputsignal. Similarly, in tubes which employ a grid structure forcontrolling the beam density, there is provided an accelerating anode.It is readily apparent that when the intensity of the beam is varied toderive a desired variation in beam intensity as, for example, in thederivation of shaped output pulses such as Gaussian pulses or amplitudemodulated output signal, the side effect is to also provide a variationin beam velocity. The variation in beam velocity affects the phase ofthe output of the radio frequency section associated with the beam.Between the minimum current density and the maximum current density,there may be a considerable phase shift which, of course, distorts theoutput pulse or signal.

It is, therefore, a general object of this invention to provideapparatus and method for neutralizing the phase shift due to velocityvariation in the beam of a beam'type tube.

It is another object of this invention to provide an apparatus andmethod for neutralizing phase shift due to velocity variation of amodulated beam type beam tube such as a klystron including a modulatinganode or other modulating electrode.

It is a more particular object of this invention to provide an apparatusand method to neutralize velocity variation type phase shift in beamtype tubes by providing an external feedback circuit which is responsiveto the beam current.

These and other objects and features of the invention will become moreclearly apparent upon a review of the following description inconjunction with the accompanying drawings.

Referring to the drawing:

FIGURE 1 is a schematic diagram of a beam projection and interceptionmeans with one feedback circuit; and

FIGURE 2 is a schematic diagram of a beam projection and interceptionmeans with another feedback circuit.

Referring to FIGURE 1, there is shown an electron gun 11 for a beam typetube. The gun includes a cathode 13 heated by a filament 15 and situatedWithin a focusing electrode 17. The cathode 13 and focusing electrode 17are connected to the cathode terminal 19. Disposed in front of thecathode 13 is a modulating anode 21 and an accelerating anode 23. Radiofrequency structures may be disposed to interact with the beam, forexample, in a klystron. Various resonators and cavities are disposedalong the beam. A radio frequency structure is not shown in the drawingsince it is not deemed to importance to the instant invention. However,a collector 25 is shown at the opposite end of the 'klyst-ron unit inaxial alignment with the cathode 13 and the anodes 21 and 23. Thecollector interrupts and collects the beam.

An inductor 27 is connected to the cathode terminal 19 and the oppositeend of the inductor is coupled through the parallel connected capacitor29 and power supply 31 to the accelerating anode 23. Also connectedbetween the inductor 27 and the anode 23 is a pair of series switchingtubes 33 and 35. The junction of the anode of tube 33 and cathode oftube 35 is connected to the modulating anode 21. Modulating voltages maybe applied to the grids of the tubes 3-3 and 35 in conventional mannerto modulate the beam current.

A capacitor 37 and a resistor 39 are serially connected between thecathode terminal 19 and the anode 23. The junction of the capacitor 37and the resistor 39 is connected to a source of positive voltage B+through vacuum tube 41. The grid is controlled by a voltage appliedthrough transformer 43, the secondary of which is connected between thegrid and cathode of tube 41. The primary of the transformer is connectedbetween the positive terminal of the power supply 31 and the collector25. It will be apparent to one skilled in the art that a solid statedevice may be substituted for the tube 41.

In normal operation of the beam-type device similar to that shown (butignoring the inductor 27, capacitor 37, resistor 39, tube 41 andtransformer 43), the electron beam 45, as it passes through the anodes21 and 23, includes a substantial negative charge to the electronswithin the beam itself. As modulating voltage is applied by themodulating anode 21 to vary the beam current, the beam acceleration dueto the fields from the accelerating anode changes. As the beam becomesdenser, the electrons near the outer perimeter of the beam 45 areaffected by the accelerating voltages to a greater degree than thoseelectrons near the center of the beam which are relatively isolated fromthe accelerating voltage. Thus, the

' outer portion of the beam is accelerated to a greater extent than theinner portion. The velocity of the electrons varies from the inner tothe outer portion of the beam. As the beam intensity is varied under theinfluence of the modulating anode, the degree of penetration, thusacceleration changes and there is a change in the average velocity ofthe beam, as previously described.

Since phase shift in the output of the radio frequency section is causedby the change in beam velocity, the phase shift is proportional to thebeam density. The beam density may be easily detected at the collector25 and, in accordance with this invention, is used as a feedback signalto neutralize the phase shift. The beam density is controlled bycontrolling the degree of conduction of each of the tubes 33 and 35.

In accordance with the invention, a feedback signal is derived whichserves to increase the accelerating voltage as the beam densityincreases whereby to maintain substantially constant beam velocity withchanging beam current. The feedback circuit, previously described,includes the collector 25 connected to the primary of a transformer 43whereby the beam current passes through the primary and induces avoltage between the grid and cathode of the tube 41 which isproportional to the current to thereby control the conduction of thetube 41. The current for the tube is supplied through the inductor 27.The voltage drop across the induct-or 27 changes and adds to orsubtracts from the accelerating voltage. The transformer 43 is phased sothat the tube 41 conducts less current as the beam current increases tothereby reduce the voltage drop in the inductor and increase theaccelerating voltage.

Another circuit for performing the same function as those shown inFIGURE 1 is shown in FIGURE 2. Like parts bear like reference numerals.Thus, the inductor 27, capacitor 29, power supply 31, tubes 33 and 35bear like reference numerals to perform the same functions. The meansfor deriving the feedback signal again comprises a transformer. Thetransformer 51 which has its primary serially connected between thepositive terminal of the power supply and the positive terminal of anauxiliary power supply or battery 52 which, in turn, has its negativeterminal connected to the collector thereby provide a depressedcollector connection. The secondary of the transformer has one terminalconnected to the positive terminal of the power supply and its otherterminal connected to the cathode lead through a capacitor 54. There isprovided a voltage limiting diode 53 between the positive terminal ofthe power supply and the common terminal of the capacitor 54 andsecondary of the transformer 51.

Operation of the circuit is to circulate a current dependent on beamcurrent in the loop including the power supply '31, secondary oftransformer 51, capacitor 54 and inductor 27. The circulating currentincreases and decreases as the beam current increases and decreases and,in turn, the accelerating voltage is controlled to maintain a constantaverage beam velocity.

Thus, there is provided a means responsive to beam current forneutralizing velocity variations in a beam resulting from the modulationof the beam density.

I claim:

1. A circuit for eliminating phase shift due to velocity variationarising from variations in beam density in a beam tube having anaccelerating means, a cathode and a collector, means for applying anaccelerating voltage to said accelerating means, and feedback meansresponsive to the intensity of said beam connected between saidcollector and said accelerating means for varying said acceleratingvoltage in direct proportion to the said variations in beam density.

2. In an electron beam type tube of the type which includes a cathode,an accelerating anode for accelerating electrons leaving the cathode, abeam current modulating electrode for modulating the beam current, and acollector for intercepting the beam, means for applying an acceleratingvoltage between the cathode and anode, means for applying a modulatingvoltage between said cathode and said modulating electrode, and meansresponsive to the collector current for varying the accelerating voltagebetween the cathode and anode in direct proportion to the beam currentto neutralize velocity variations in the beam due to variations in beamcurrent.

3. A circuit for minimizing phase shift due to velocity variationarising from variations in beam density in'a beam tube including acathode and a collector between which an electron beam is projected,accelerating means for controlling the beam velocity, means for applyingan accelerating voltage to said accelerating means, and feedback meansresponsive to the density of said beam connected between said collectorand said accelerating means for varying the accelerating voltage appliedto said accelerating means in direct proportion to said variations inbeam density.

4. In an electron beam type tube of the type which includes a cathode,an accelerating anode for accelerating electrons leaving the cathode, abeam current modulating means for modulating the beam current, and acollector for intercepting the beam, means for applying an acceleratingvoltage between the cathode and anode, and means responsive to thecollector current for varying the accelerating voltage between thecathode and anode in direct proportion to said beam current toneutralize velocity variations in the beam due to variations in beamcurrent density.

5. A circuit for minimizing phase shift due to velocity variationsarising from beam density variations in a beam tube including a cathodeand a collector between which an electron beam is projected,accelerating means for controlling the beam velocity, means for applyingan accelerating voltage to the accelerating means, and feedback meansincluding the primary windings of a transformer connected in thecollector current path, and means associated with the secondary windingsof said transformer for varying the voltage applied to said acceleratinganode.

6. A circuit as in claim 5 wherein said means associated with thesecondary winding of the transformer comprises an inductor connected inseries with said means for applying an accelerating voltage to saidaccelerating means, and means for causing current to flow in saidinductor in response to changes in beam current.

7. An electron beam type tube including a cathode, an accelerating anodefor accelerating electrons leaving the cathode, a modulating anodedisposed in the electron path between the cathode and acceleratinganode, means for controlling the voltage on the modulating anode tomodulate the beam current, a collector spaced from the acceleratinganode and serving to collect the electrons, means for applying anaccelerating voltage between the cathode and accelerating anode, andmeans responsive to the collector current for varying the acceleratingvoltage in direct proportion to said beam current to neutralize velocityvariations in the beam due to variations in beam density.

8. An electron beam type tube as in claim 7 wherein said last namedmeans includes a transformer having primary and secondary windings, saidprimary windings being connected in the collector current path and saidsecondary winding being connected in circuit with means for varying theaccelerating voltage responsive to beam current density.

References Cited by the Examiner UNITED STATES PATENTS 2,229,700 1/1941Hollmann 328--23l X 2,808,470 10/1957 Hansell 33044 3,108,232 10/1963Bartram 330-44 ROY LAKE, Primary Examiner.

N. KAUFMAN, A. L. BRODY, Assistant Examiners.

1. A CIRCUIT FOR ELIMINATING PHASE SHIFT DUE TO VELOCITY VARIATIONARISING FROM VARIATIONS IN BEAM DENSITY IN A BEAM TUBE HAVING ANACCELERATING MEANS, A CATHODE AND A COLLECTOR, MEANS FOR APPLYING ANACCELERATING VOLTAGE TO SAID ACCELERATING MEANS, AND FEEDBACK MEANSRESPONSIVE TO THE INTENSITY OF SAID BEAM CONNECTED BETWEEN SAIDCOLLECTOR AND SAID ACCELERATING MEANS FOR VARYING SAID ACCELERATINGVOLTAGE IN DIRECT PROPORTION TO THE SAID VARIATIONS IN BEAM DENSITY.